Method and apparatus for generating pilot tone in orthogonal frequency division multiplexing access system, and method and apparatus for estimating channel using it

ABSTRACT

The present invention relates to a pilot tone generating method and apparatus of an orthogonal frequency division multiple access system and method, and a channel estimation method and apparatus using the same. The channel estimation apparatus includes a pilot tone extracting unit for extracting a pilot tone, which is inserted within a frame with data tone, masked with an orthogonal code; a pilot tone unmasking unit for unmasking of the pilot tone extracted from the pilot tone extracting unit by using an orthogonal code information; and a channel estimation operating unit for estimating a channel by calculating an average of the pilot tones which is unmasked in the unmasking unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/288,093, filed Oct. 7, 2016, which is a continuation of U.S.application Ser. No. 14/550,160, filed Nov. 21, 2014, now U.S. Pat. No.10,819,480, issued Oct. 27, 2020, which is a divisional of U.S.application Ser. No. 14/065,976, filed Oct. 29, 2013, now U.S. Pat. No.9,276,719, issued Mar. 1, 2016, which is a continuation of U.S.application Ser. No. 12/521,370, filed Jun. 26, 2009, now U.S. Pat. No.8,588,274, issued Nov. 19, 2013, which is a National Stage Entry ofInternational Application No. PCT/KR2007/006761, filed Dec. 21, 2007,and claims the benefit of priority from Korean Patent Application No. KR10-2006-0135417, filed Dec. 27, 2006. The entire contents of all of theaforementioned applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an OFDM/OFDMA (Orthogonal FrequencyDivision Multiplexing/Orthogonal Frequency Division Multiplexing Access)transmission system, more particularly, to the method and apparatus forgenerating a pilot tone capable of eliminating an interference by userswithin a different cells or sectors in an OFDMA system, and the channelestimation method and apparatus corresponding to it.

BACKGROUND ART

OFDM or OFDMA which is based it is a multicarrier modulation schemewhich parallelly transmits data by using a multiple orthogonalsubcarriers instead of a single carrier having a broad band. It is basedon the fact that each subchannel of a narrowband has the flat fadingcharacteristic in the frequency selective fading channel having the verylarge ISI (Inter-Symbol Interference).

In OFDM, as the symbol is determined on the frequency domain, it isnecessary to have an equalizer for frequency domain in order tocompensate for the channel distortion of the received symbol. For this,in addition to sending data symbol, the transmitter of the OFDMtransmission system transmits the pilot symbol used for the channelestimation for the equalization of data symbol by estimating thecharacteristics of the channel transmitting a signal.

FIG. 1 is a block diagram that shows the configuration OFDM receiver ofthe related art, showing schematically only the unit that restores datafrom the baseband signal obtained from the received signal.

A burst symbol extracting unit 100 extracts the OFDM symbol from thebaseband signal obtained from the received signal by the RF (RadioFrequency) processing unit (not shown). As to the OFDM symbol which isextracted by the burst symbol extracting unit 100, it is applied to anequalizer 108, after the CP (Cyclic Prefix) which is inserted by a CPdeleting unit 102 from the transmitter is eliminated and FFT (FastFourier Transform) is performed by an FFT unit 104. The equalizer 108compensates for the channel distortion according to the channelcharacteristic value which is estimated by a channel estimating unit 106for the FFT data signal.

After being demodulated in a demodulator 110, the signal compensated thechannel distortion performs Viterbi decoding by a decoder 112 and dataare restored by the determination of a deciding unit 114. The channelestimating unit 106 performs the channel estimation by using the pilottone. Pilot tones are arranged between OFDM data tones. In the meantime,when the channel is estimated, the pilot tone is interfered by the pilottones from the cell of the adjacent base station or other user of thesector. Therefore, the pilot tone interference cancellation technologycapable of the exact channel estimation in spite of the interferencesignal is required.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, an object of the present invention is to solve at least theproblems and disadvantages of the related art. The present invention isto provide the pilot tone generating method and apparatus in anorthogonal frequency division multiple access system capable ofgenerating the pilot tone for the exact channel estimation without theinterference of the pilot tone of the adjacent base station that affectsthe pilot tone.

Another object of the present invention is to provide the channelestimation method and apparatus using the pilot tone generating methodand apparatus in the orthogonal frequency division multiple accesssystem.

Technical Solution

In order to accomplish the object, according to an aspect of the presentinvention, provided is a pilot tone generating method in an orthogonalfrequency division multiple access system which uses for subcarriershaving an orthogonality and transmits data by frame, which comprises thesteps of: (a) inserting a data tone and a pilot tone into the frame; (b)PRBS (Pseudo Random Binary Sequence) masking for the data tone; and (c)masking an orthogonal code for the pilot tone.

In accordance with an aspect of the present invention, at the step (b),masking the orthogonal code for eight pilot tones forming a rectangularwindow form, when the frame is a down-link subframe. The masking of theorthogonal code is performed by moving the rectangular window from leftto right, from top to bottom, by pilot tone inserted into the frame. Aset of the orthogonal code for eight pilot tones is an eight-bitorthogonal code set having an orthogonality for a different code. At thestep (b), masking the orthogonal code for four pilot tones forming atile of an up-link subframe, when the frame is the up-link subframe. Aset of the orthogonal code for four pilot tones is a four-bit orthogonalcode set having an orthogonality for a different code. At the step (c),the masking is performed by allocating the same orthogonal code tosectors within each cell and allocating a different orthogonal code tothe each cell, when FRF (Frequency Reuse Factor)-3 is applied. At thestep (c), the masking is performed by allocating a different orthogonalcode to each sector within a cell, when FRF (Frequency Reuse Factor)-1is applied. After the step (c), an aspect of the present inventionfurther comprises the step (d) transmitting the masked orthogonal codeinformation. At the step (d), the orthogonal code information isincluded in a DCD TLV (Downlink Channel Descriptor Type, Length, Value)field of a NBR-ADV message (Neighbor Advertisement Message).

According to another aspect of the present invention, provided is apilot tone generating apparatus of an orthogonal frequency divisionmultiple access (OFDMA) system, which comprises a data and pilotinserting unit for inserting a data tone and a pilot tone into a frameof the OFDMA system; a PRBS (Pseudo Random Binary Sequence) masking unitfor masking a PRBS for the data tone; and an orthogonal code maskingunit for masking an orthogonal code for the pilot tone.

The orthogonal code masking unit masks the orthogonal code for eightpilot tones forming a rectangular window form when the frame is adown-link subframe, and masks the orthogonal code for four pilot tonesforming a tile of an up-link subframe when the frame is the up-linksubframe. The orthogonal code masking unit masks the orthogonal code bymoving the rectangular window from left to right, from top to bottom, bypilot tone inserted into the frame. The orthogonal code masking unitmasks the orthogonal code by allocating the same orthogonal code tosectors within each cell and allocating a different orthogonal code tothe each cell, when FRF (Frequency Reuse Factor)-3 is applied. Theorthogonal code masking unit masks the orthogonal code by allocating adifferent orthogonal code to each sector within a cell, when FRF(Frequency Reuse Factor)-1 is applied.

According to still another aspect of the present invention, provided isa channel estimation method by using a pilot tone in a receiverreceiving an orthogonal frequency division multiple signal by frame,which comprises the steps of: (a) extracting a pilot tone, whichcorresponds to a channel for estimating, masked with an orthogonal codefrom a received signal; (b) unmasking the extracted pilot tone; and (c)estimating a channel by calculating an average of the unmasked pilottones.

At the step (b), unmasking the masked orthogonal code for eight pilottones forming a rectangular window form when the frame is a down-linksubframe. The unmasking of the orthogonal code is performed by movingthe rectangular window from left to right, from top to bottom, bychannel. At the step (b), unmasking the masked orthogonal code for fourpilot tones forming a tile of up-link subframe, when the frame is theup-link subframe. At the step (b), the unmasking is performed by usingthe orthogonal code information received before the step (a). Theorthogonal code information is an orthogonal code masking informationwhich is included in a NBR-ADV message (Neighbor Advertisement Message)field.

According to still another aspect of the present invention, provided isa channel estimation apparatus for estimating a channel by using a pilottone in an orthogonal frequency division multiple access system, whichcomprises a pilot tone extracting unit for extracting, a pilot tone,which is inserted within a frame with data tone, masked with anorthogonal code; a pilot tone unmasking unit for unmasking of the pilottone extracted from the pilot tone extracting unit by using anorthogonal code information; and a channel estimation operating unit forestimating a channel by calculating an average of the pilot tones whichis unmasked in the unmasking unit.

The unmasking unit unmasks the masked orthogonal code for eight pilottones forming a rectangular window form when the frame is down-linksubframe, and unmasks the masked orthogonal code for four pilot tonesforming a tile of an up-link subframe when the frame is the up-linksubframe. The pilot tone unmasking unit unmasks the masked orthogonalcode by moving the rectangular window from left to right, from top tobottom, by channel.

Advantageous Effects

According to the present invention, even when the interference signalexists, the relatively exact channel estimation is possible by using anorthogonal code so that the portable Internet (WiBro/WiMax) systemperformance can be improved. Particularly, in a channel estimation, aninterference between users that is the interference by the users ofother cell or sector can be eliminated. Further, a much more performanceimprovement can be implemented as the signal can be coherently combinedin a diversity combining. Additionally, the interference power can beaccurately measured as far as possible, so that the performance of CINR(Carrier Interference to Noise Ratio) measurement can be improved.

The present invention can be applied to the OFDM system including theWiBro system. And even if the orthogonal code is moved to the time andfrequency axis, the orthogonality is still maintained so that asuccessive channel estimation is possible. Further, the size of theorthogonal code window is determined by the coherence time and thecoherence bandwidth. By measuring the power loaded in a coding wordexcept the desired orthogonal code word, the interference power can beeasily calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary features, aspects, and advantages of thepresent invention will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram that shows the configuration of OFDM receiverof the related art;

FIG. 2 is a block diagram that shows the configuration of an example ofan OFDM wireless communication system transmitter applying the pilottone generating method and apparatus in an orthogonal frequency divisionmultiple access system according to the present invention;

FIG. 3 is a block diagram that shows the configuration of the pilot tonegenerating apparatus in an orthogonal frequency division multiple accesssystem according to the present invention;

FIG. 4 shows an example of an OFDMA TDD frame structure according to theIEEE. 802.16e standards;

FIG. 5 shows an example of an orthogonal code set for eight pilot tones;

FIG. 6 shows a rectangular window which is performed while moving fromleft to right, from top to bottom, by the pilot tone unit forming adown-link subframe;

FIG. 7 shows an example of an orthogonal code set for four pilot tones;

FIG. 8 is a flowchart that shows the pilot tone generating method in anorthogonal frequency division multiple access system according to thepresent invention;

FIG. 9 shows an example of a rectangular window comprised of eight pilottones forming the rectangular window form in case of down-link subframe;

FIG. 10 shows a tile comprised of four pilot tones in case of up-linksubframe;

FIG. 11 is a block diagram that shows the configuration of an example ofa receiver in an OFDM wireless communication system applying the channelestimating method and apparatus of an orthogonal frequency divisionmultiple access system according to the present invention;

FIG. 12 is a block diagram that shows the configuration of a channelestimation apparatus in an orthogonal frequency division multiple accesssystem according to the present invention;

FIG. 13 is a flowchart that shows the channel estimation method in theorthogonal frequency division multiple access system according to thepresent invention;

FIG. 14 shows an example of the orthogonal code allocation within a cellwhich is not sectored with the FRF (Frequency Reuse Factor)-1;

FIG. 15 shows the orthogonal code allocation within a cell which issectored with the FRF-1. The code is assigned in order that the samecode is allocated to be far away each other as far as possible so thatthe interference may be minimized;

FIG. 16 shows the orthogonal code allocation in the cell which issectored with the FRF-3;

FIGS. 17 and 18 show that the orthogonal code word information field isadded to the NBR-ADV message (Neighbor Advertisement Message)transmitted and received in the hand-over;

FIGS. 19 and 20 show that the orthogonal code word information is addedto the UCD (Uplink Channel Descriptor) TLV field.

MODE FOR THE INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings. The same elementswill be designated by the same reference numerals all through thefollowing description and drawings although they are shown in differentdrawings. Further, in the following description of the presentinvention, a detailed description of known functions and configurationsincorporated herein will be omitted when it may make the subject matterof the present invention rather unclear.

Firstly, the pilot tone generating method and apparatus in theorthogonal frequency division multiple access system will beillustrated.

FIG. 2 is a block diagram that shows the configuration of an example ofan OFDM (Orthogonal Frequency Division Multiplexing) wirelesscommunication system transmitter applying the pilot tone generatingmethod and apparatus of an orthogonal frequency division multiple accesssystem according to the present invention. The transmitter includes anencoder 202, a symbol mapping unit 204, a serial/parallel converter 206,a symbol inserting unit 208, an IFFT (Inverse Fast Fourier Transform)unit 210, a parallel/serial converter 212, a CP (Cyclic Prefix)inserting unit 214, a D/A (Digital/Analog) converter 216 and an RF(Radio Frequency) processing unit 218.

If a user data is inputted to the encoder 202, after coding the inputteduser data, the encoder 202 outputs the user data to the symbol mappingunit 204. Here, the coding scheme performed in the encoder 202 can bethe turbo coding scheme having the coding rate or the convolutionalcoding scheme. The symbol mapping unit 204 modulates the coded bitoutputted from the encoder 202 with a corresponding modulation schemeand generates the modulation symbol to output to the serial/parallelconverter 206.

Here, the BPSK (Binary Phase Shift Keying), the QPSK (Quadrature PhaseShift Keying) scheme, 16QAM (Quadrature Amplitude Modulation) or 64QAMscheme can be used for the modulation scheme.

After inputting the series modulation symbols outputted from the symbolmapping unit 204, the serial/parallel converter 206 paralleltransforming them, and outputting them to the symbol inserting unit 208.The symbol inserting unit 208 inserts data symbols and pilot symbolsinto the modulated parallel transformed symbols which are outputted fromthe serial/parallel converter 206, outputting to the IFFT unit 210,after performing the PRBS (Pseudo Random Binary Sequence) masking andthe orthogonal code masking sequentially. After inputting the signaloutputted from the symbol inserting unit 208 and performing the N-pointIFFT, the IFFT unit 210 outputs to the parallel/serial converter 212.

The parallel/serial converter 212 inputs the signal outputted from theIFFT unit, and outputting to the CP inserting unit 214 after a serialtransformation. After inputting the signal outputted from theparallel/serial converter 212 and inserting the CP signal, the CPinserting unit 214 outputs to the D/A converter 216. The CP is insertedin order to eliminate the interference between the OFDM symboltransmitted in the previous OFDM symbol time and the present OFDM symbolwhen transmitting the OFDM symbol in an OFDM communication system. Afterinputting the signal outputted from the CP inserting unit 214 andconverting into the analog, the D/A converter 216 outputs to the RFprocessing unit 218. The RF processing unit 218 including a filter and apreprocessor performs RF processing of the signal outputted from the D/Aconverter 216 in order to actually can be transmitted on-air, andtransmits on-air through a transmission antenna.

FIG. 3 is a block diagram that shows the configuration of the pilot tonegenerating apparatus in an orthogonal frequency division multiple accesssystem according to the present invention, corresponding to the pilotsymbol inserting unit 208 of FIG. 2. The pilot tone generating apparatusincludes a data and pilot inserting unit 300, a PRBS masking unit 340and an orthogonal code masking unit 350. The data and pilot insertingunit 300 insert the data tone and pilot tone into the frame of theorthogonal frequency division multiple access system.

FIG. 4 shows an example of an OFDMA (Orthogonal Frequency DivisionMultiple Access) TDD (Time Division Duplexing) frame structure accordingto the IEEE 802.16e standards. The frame includes a DL (Down Link)subframe and an UL (Up Link) subframe.

Referring to FIG. 4, the first symbol of DL subframe is allocated aspreamble and such preamble is used for the frame synchronization and thecell identification. The TTG (Tx/Rx Transition Gap) is inserted betweenDL subframe and UL subframe and the RTG (Rx/Tx Transition Gap) isinserted between the frame end and beginning. Additionally, the initialfour subchannel of two OFDMA symbols which are transmitted immediatelyafter the preamble includes the FCH (Frame Control Header) of twentyfour bits for transmitting the frame constitution information. Such DLsubframe can be comprised of a plurality of zones. Each zone can bechanged by the OFDMA symbols while being classified by the OFDMAsubchannel assignment scheme. The subchannel assignment scheme includesthe PUSC (Partial Usage of Subchannels), the FUSC (Full Usage ofSubchannels), Band-AMC.

Further, in the OFDMA system, data are transmitted to UL through thesubchannel allocated by each subscriber. Such UL subframe can becomprised of a plurality of zones. Like the DL, each zone is classifiedby the OFDMA subchannel assignment scheme, and can be changed by theOFDMA symbol. The subchannel assignment scheme of UL includes UL-PUSC,UL-OPUSC, and UL Band AMC.

Additionally, the ranging subchannel illustrated in the lower portion ofUL subframe illustrated in FIG. 4 is used for UL synchronizationacquisition and the power control between the base stations of a mobileterminal, and the bandwidth demand of a mobile terminal. In the WiBro,four kinds of mode including the initial ranging, the periodic ranging,the hand-off ranging, and the bandwidth request ranging are defined. Inthe UL, the synchronization is performed through the ranging process. Insuch UL, the time point of receiving signal can be changed as thechannel environment is different in each mobile terminal, and themagnitude of received power can be changed. In case of the UL signal,the base station has to estimate the channel for each user since thebase station receives the signal of the different mobile terminal thathas passed through other channel environment.

The PRBS masking unit 340 performs the PRBS masking for the data tone.The PRBS masking is performed by using the PRBS value (X¹¹+X⁹+1) whichis generated from the PRBS generator. The orthogonal code masking unit350 performs the masking of the orthogonal code for the pilot tone. Whenit is the DL subframe, it is desirable that the orthogonal code maskingunit 350 performs the masking of the orthogonal code for the adjacenteight or four pilot tone forming the rectangular window form. An exampleof the orthogonal code set for eight pilot tones is the same as FIG. 5,and an example of the orthogonal code set for four pilot tones is thesame as FIG. 7.

Additionally, as shown in FIG. 6, the orthogonal code masking isinserted into the DL subframe, while moving the rectangular window fromleft to right, from top to bottom, by the adjacent eight pilot tones toperform. In FIG. 6, each codeword can be allocated one by one for eachbase station. Further, when the orthogonal code masking unit 350 is theUL subframe, the orthogonal code is masked for four pilot tones formingthe tile of the UL subframe.

As shown in FIGS. 5 and 7, it can be known that the codes used in thepresent invention has an orthogonality. FIG. 6 shows the case of 2×4window size, while other window size also can be shown. It is shown thatthe orthogonality is established even when the window is moved to rightand downwards from the orthogonal codeword one to eight.

FIG. 8 is a flowchart that shows the pilot tone generating method in anorthogonal frequency division multiple access system according to thepresent invention.

Firstly, the data tone and the pilot tone are inserted into the frame ofthe orthogonal frequency division multiple access system formed throughthe serial/parallel converter 302 (S800), and then, PRBS masking for thedata tone (S840). Subsequently, the orthogonal code is masked for thepilot tone (S850). In detail, in case of the DL subframe, the orthogonalcode is masked for eight pilot tones which form the rectangular windowform as shown in FIG. 9. As shown in FIG. 7, the orthogonal code maskingcan be performed, while moving the rectangular window from left toright, from top to bottom, by the pilot tone inserted into the frame.The orthogonal code set for the eight pilot tones is the same as FIG. 5.When the frame is the UL subframe, as shown in FIG. 10, the masking ofthe orthogonal code is performed for four pilot tones forming the tileof the UL subframe. The orthogonal code set for the four pilot tone isthe same as FIG. 7.

In the meantime, FIG. 11 is a block diagram that shows the configurationof an example of a receiver of an OFDM wireless communication systemapplying the channel estimating method and apparatus in an orthogonalfrequency division multiple access system according to the presentinvention. The receiver includes a RF processing unit 1102, an A/Dconverter 1104, a CP deleting unit 1106, a serial/parallel converter1108, an FFT unit 1110, a pilot symbol extracting unit 1112, a channelestimating unit 1114, an equalizer 1116, a parallel/serial converter1118, a symbol demapping unit 1120 and a decoder 1122.

The receiver has the reverse direction structure of transmitter shown inFIG. 2. The signal transmitted from the transmitter is received by areceive antenna of the receiver with adding the noise after passingthrough a multipath channel. The signal received through the receiveantenna is inputted to the RF processing unit 1102, and the RFprocessing unit 1102 outputs the signal received through the receiveantenna to the A/D converter 1104 after down converting into theintermediate frequency band. After converting the analog signaloutputted from the RF processing unit 1102 into the digital signal, theA/D converter 1104 outputs to the CP deleting unit 1106.

The CP deleting unit 1106 outputs to the serial/parallel converter 1108,after inputting the signal outputted from the A/D converter 1104 andeliminating the CP signal. The serial/parallel converter 1108 performsthe N-point FFT through the FFT unit 1110 for the serial signaloutputted from the CP deleting unit 1106, thereafter, outputting to theequalizer 1116 and the pilot symbol extracting unit 1112. Afterinputting the signal outputted from the FFT unit 1116 andchannel-equalizing, the equalizer 1116 outputs to the parallel/serialconverter 1118. The parallel/serial converter 1118 outputs to the symboldemapping unit 1120, after inputting the parallel signal outputted fromthe equalizer 1116 for serial transforming.

In the meantime, the signal outputted from the FFT unit 1110 is inputtedto the pilot symbol extracting unit 1112. The pilot symbol extractingunit 1112 detects the pilot symbols in the signal outputted from the FFTunit 1110 and outputs the detected pilot symbols to the channelestimating unit 1114. By utilizing the pilot symbols outputted from thepilot symbol extracting unit 1112, the channel estimating unit 1114performs the channel estimation and outputs the channel estimationresult to the equalizer 1116. The terminal receiver generates the CQI(channel quality information) corresponding to the channel estimationresult of the channel estimating unit 1114, transmitting the generatedCQI through the CQI transmitter (not shown) to the transmitter.

After demodulating the signal outputted from the parallel/serialconverter 1118 by a corresponding demodulation scheme, the symboldemapping unit 1120 outputs to the decoder 1122. The decoder 1122outputs a final received data, after decoding the signal outputted fromthe symbol demapping unit 1120 by a corresponding decoding scheme. Here,the demodulation scheme and the decoding scheme corresponds to themodulation scheme and the coding scheme that are applied by thetransmitter.

FIG. 12 is a block diagram that shows the configuration of a channelestimation apparatus in an orthogonal frequency division multiple accesssystem according to the present invention, corresponding to the pilotsymbol extracting unit 1112 and channel estimating unit 1114 of FIG. 11.The channel estimation apparatus includes a pilot tone extracting unit1210, an unmasking unit 1220 and a channel estimation operating unit1230.

The pilot tone extracting unit 1210 extracts the pilot tone masked withthe orthogonal code in the transmitting side, which corresponds to thechannel for estimating with the received signal which is Fouriertransformed. The unmasking unit 1220 performs the unmasking of theextracted pilot tone.

In case of the DL, it is desirable that the unmasking unit 1220 performsthe unmasking of the orthogonal code which is masked tor the adjacenteight pilot tones forming the rectangular window form among the pilottones inserted into the DL subframe.

As shown in FIG. 6, the unmasking of the orthogonal code is performedfor the frame into which the pilot tone is inserted by moving therectangular window from left to right, from top to bottom. In case ofUL, the unmasking unit 1220 forms the tile of the UL subframe, andperforms the unmasking of the orthogonal code for four pilot tones whichis masked with the orthogonal code. The channel estimation operatingunit 1230 estimates a channel by performing the averaging of theunmasked pilot tones.

FIG. 13 is a flowchart that shows the channel estimation method in theorthogonal frequency division multiple access system according to thepresent invention.

Firstly, the pilot tone, corresponding to the channel for estimating,masked with the orthogonal code is extracted from the received signalwhich is Fourier transformed (S1310). Then, the extracted pilot tone isunmasked (S1320). In case of down-link, the orthogonal code masked foreight pilot tones forming the rectangular window form is unmasked, and,as shown in FIG. 6, the rectangular window performs smoothing by channelfrom left to right, from top to bottom. Further, in case of up-link, theorthogonal code is unmasked for the four pilot tones masked with theorthogonal code. Then, the averaging of the unmasked pilot tones isperformed to estimate a channel (S1330).

In the meantime, for an example of the UL subframe, the channelestimation of the present invention will be described in detail. In theIEEE 802.16e (Wibro), the pilot tone is positioned in the corner of asquare in the tile forming the UL subframe. The pilot tone that maskedthe orthogonal code of the present invention is generated as follows.

When the orthogonal code for the pilot tone forming the tile of the ULsubframe for channel estimation in a receiving side is 1 1 1 1, thepilot tone of the tile masked with the orthogonal code becomes A A A A(Here, A is the intensity of the pilot tone signal). In the meantime, incase the orthogonal code for the pilot tone forming the tile of the ULsubframe for the cell or sector which are adjacent to the cell or sectorto which the tile belongs is 1 −1 1 −1, the masked pilot tone of thetile masked with the orthogonal code becomes A −A A −A.

In the meantime, the process that the pilot tone generated in atransmitter is used for the channel estimation in a receiver. Firstly,pilot tones masked with the orthogonal code is extracted in thereceiver. When the signal intensity faded in a radio channel is B andthe phase change is θ, the pilot tone signal masked with the orthogonalcode 1 1 1 1 in the transmitter becomes Be^(jθ) Be^(jθ) Be^(jθ) Be^(jθ).

In the meantime, the pilot tone signal masked with the orthogonal code 1−1 1 −1 in the transmitter of the adjacent cell or sector becomesCe^(jΦ) −Ce^(jΦ) Ce^(jΦ) −Ce^(jΦ), when the signal intensity faded in aradio channel is C and the phase change is Φ. In this way, when theunmasking for the pilot tone is performed in the receiver, the unmaskedpilot tone becomes Be^(jθ) Be^(jθ) Be^(jθ) Be^(jθ), and the pilot toneof the adjacent cell or sector becomes Ce^(jΦ) −Ce^(jΦ) Ce^(jΦ) −Ce^(jΦ)since the orthogonal code of the cell for channel estimation continueswith 1 1 1 1. By averaging them, the channel in data tone for channelestimation can be estimated. That is, it becomes the following Equation1.

$\begin{matrix}\begin{matrix}{{{The}\mspace{14mu}{estimated}\mspace{14mu}{pilot}\mspace{14mu}{tone}} = {{\left( {{Be}^{i\;\theta} + {Be}^{i\;\theta} + {Be}^{i\;\theta} + {Be}^{i\;\theta}} \right)/4} +}} \\{\left( {{Ce}^{j\;\Phi} - {Ce}^{j\;\Phi} + {Ce}^{j\;\Phi} - {Ce}^{j\;\Phi}} \right)/4} \\{= {Be}^{j\;\theta}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

As shown in Equation 1, since the pilot tone is masked with theorthogonal code in the transmitter, in the channel estimating, theinterference of the pilot tone in the adjacent cell or sector iseliminated due to the orthogonality. Similarly, in case of DL, theinterference of the adjacent cell or sector is eliminated when it ismasked with the orthogonal code under the same principles as UL.

In the present invention, all base stations can use the same PRBS, whileother orthogonal code sequence can be applied for the pilot subcarrierused in the channel estimation for each cell or sector. The interferencefrom other user is eliminated by using an orthogonality in channelestimating, by applying the PRBS for data tone, and by applying theorthogonal code used in the present invention for the pilot subcarrier.Moreover, different users can be distinguished by using the orthogonalcode after applying the same PRBS to the pilot subcarrier by eachpermutation scheme.

FIG. 14 shows an example of the orthogonal code allocation within a cellwhich is not sectored with the FRF (Frequency Reuse Factor)-1. A code isassigned to minimize the interference between cells by assigning adifferent orthogonal code to each cell.

FIG. 15 shows the orthogonal code allocation within a cell which issectored with the FRF-1. The code is assigned in order that the samecode is allocated to be far away each other as far as possible so thatthe interference may be minimized.

FIG. 16 shows the orthogonal code allocation in the cell which issectored with the FRF-3. In case of FRF-3, since the frequency band isphysically divided into three, the interference does not affect evenwhen the same orthogonal code is used in the same cell, therefore, acode is assigned like FIG. 14.

FIGS. 17 and 18 show that the orthogonal code word information field isadded to the NBR-ADV message (Neighbor Advertisement Message)transmitted and received in the hand-over. The present inventionprovides orthogonal code word information of the cell or sector that ishand-overed by adding the orthogonal code word information, that is, theorthogonal code set one to set eight to the DCD (Downlink ChannelDescriptor) TLV (Type, Length, Value) field.

FIGS. 19 and 20 show that the orthogonal code word information is addedto the UCD (Uplink Channel Descriptor) TLV field. The DCD TLVinformation that is delivered to the NPR-ADV message in a hand-over isused by adding an orthogonal codeword information bit to the DCD TLV.Additionally, in the network entry, the terminal performs the crosscorrelation for eight orthogonal codewords to find.

Meanwhile, functions used in an apparatus and a method disclosed in thepresent specification can be embodied in storage media that a computercan read as codes that the computer can read. The storage media that thecomputer can read, include all sorts of record devices in which datathat can be read by a computer system is stored. Examples of the storagemedia that the computer can read, include ROMs, RAMs, CD-ROMs, magnetictape, floppy discs, optic data storage devices, etc., and also, includethings embodied in the form of carrier wave (e.g., transmission throughthe internet). Furthermore, the storage media that the computer can readis distributed in a computer system connected with networks. Then, thecodes that the computer can read, are stored in the distributed storagemedia in a distribution scheme, and the codes can be executed in thedistribution scheme.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention.Therefore, the spirit and scope of the present invention must be definednot by described embodiments thereof but by the appended claims andequivalents of the appended claims.

The invention claimed is:
 1. A method of transmitting signals in awireless communication system, comprising: generating a signal with asequence; selecting an orthogonal sequence based on a set of orthogonalsequences represented by an n×n matrix, n being a positive integer,wherein rows of the matrix constitute the orthogonal sequences;generating a pilot with the orthogonal sequence; and transmitting thesignal in an Orthogonal Frequency Division Multiplexing (OFDM) symbol ofa resource block, and transmitting the pilot in another OFDM symbol ofthe resource block, wherein: the resource block comprises a plurality ofsubcarriers in a frequency domain and a plurality of OFDM symbols in atime domain, respectively; at least two subcarriers on which the pilotis transmitted are either the same subcarrier or non-adjacentsubcarriers in the frequency domain and are respectively on OFDM symbolsthat are either non-adjacent OFDM symbols or the same OFDM symbol in thetime domain within the resource block; at least two subcarriers on whichthe pilot is transmitted are on one of the plurality of OFDM symbols ofthe resource block; and the pilot is transmitted: on at least three ofthe plurality of OFDM symbols of the resource block, and on subcarriersthat include a subcarrier of a highest frequency and a subcarrier of alowest frequency in the frequency domain respectively on the at leastthree OFDM symbols within the resource block.
 2. The method of claim 1,wherein the orthogonal sequence distinguishes different users.
 3. Themethod of claim 1, wherein the selecting, the generating, and thetransmitting are performed by a base station.
 4. The method of claim 1,wherein the signal and the pilot are transmitted in a downlink (DL)subframe.
 5. The method of claim 1, wherein the signal modulates acarrier or subcarrier with Binary Phase Shift Keying (BPSK) orQuadrature Phase Shift Keying (QPSK).
 6. The method of claim 1, whereinn is
 4. 7. The method of claim 1, wherein n is
 8. 8. The method of claim1, wherein n is less than or equal to
 8. 9. A transmitter in a wirelesscommunication system, comprising: a transceiver; a memory storing acomputer program; and a processor configured to call and run thecomputer program to execute: generating a signal with a sequence;selecting an orthogonal sequence based on a set of orthogonal sequencesrepresented by an n×n matrix, n being a positive integer, and generatinga pilot with the orthogonal sequence, wherein rows of the matrixconstitute the orthogonal sequences; and transmitting the signal in anOrthogonal Frequency Division Multiplexing (OFDM) symbol of a resourceblock, and transmit the pilot in another OFDM symbol of the resourceblock, wherein: the resource block comprises a plurality of subcarriersin a frequency domain and a plurality of OFDM symbols in a time domain,respectively, at least two subcarriers on which the pilot is transmittedare either the same subcarrier or non-adjacent subcarriers in thefrequency domain and are respectively on OFDM symbols that are eithernon-adjacent OFDM symbols or the same OFDM symbol in the time domainwithin the resource block, at least two subcarriers on which the pilotis transmitted are on one of the plurality of OFDM symbols of theresource block, and the pilot is transmitted: on at least three of theplurality of OFDM symbols of the resource block, and on subcarriers thatinclude a subcarrier of a highest frequency and a subcarrier of a lowestfrequency in the frequency domain respectively on the at least threeOFDM symbols within the resource block.
 10. A method of receivingsignals in a wireless communication system, comprising: receiving asignal generated with a sequence over at least one Orthogonal FrequencyDivision Multiplexing (OFDM) symbol from among a plurality of OFDMsymbols of a resource block, the resource block comprising a pluralityof subcarriers in a frequency domain and the plurality of the OFDMsymbols in a time domain; receiving a pilot generated using anorthogonal sequence over at least another OFDM symbol from among theplurality of the OFDM symbols, wherein: at least two subcarriers onwhich the pilot is transmitted are either the same subcarrier ornon-adjacent subcarriers in the frequency domain and are respectively onOFDM symbols that are either the same OFDM symbol or non-adjacent OFDMsymbols in the time domain within the resource block, at least twosubcarriers on which the pilot is transmitted are on one of theplurality of OFDM symbols of the resource block, and the pilot istransmitted: on at least two three of the plurality of OFDM symbols ofthe resource block, and on subcarriers that include a subcarrier of ahighest frequency and a subcarrier of a lowest frequency in thefrequency domain respectively on the at least three OFDM symbols withinthe resource block; and demodulating the signal using the pilot, whereinthe orthogonal sequence is selected based on a set of orthogonalsequences represented by an n×n matrix, n being a positive integer,wherein rows of the matrix constitute the orthogonal sequences.
 11. Themethod of claim 10, wherein the orthogonal sequence distinguishesdifferent users.
 12. The method of claim 10, wherein the receiving andthe demodulating are performed by a mobile terminal.
 13. The method ofclaim 10, wherein the signal is received in a downlink (DL) subframe.14. The method of claim 10, wherein the signal modulates a carrier orsubcarrier with Binary Phase Shift Keying (BPSK) or Quadrature PhaseShift Keying (QPSK).
 15. The method of claim 10, wherein n is
 4. 16. Themethod of claim 10, wherein n is
 8. 17. The method of claim 10, whereinn is less than or equal to
 8. 18. A receiver in a wireless communicationsystem, comprising: a receiving antenna configured to: receive a signalgenerated with a sequence over at least one of Orthogonal FrequencyDivision Multiplexing (OFDM) symbol from among a plurality of OFDMsymbols of a resource block, and receive a pilot generated using anorthogonal sequence over at least another OFDM symbol from among theplurality of the OFDM symbols, wherein: the resource block comprises aplurality of subcarriers in a frequency domain and the plurality of theOFDM symbols in a time domain, at least two subcarriers on which thepilot is transmitted are either the same subcarrier or non-adjacentsubcarriers in the frequency domain and are respectively on OFDM symbolsthat are either the same OFDM symbol or non-adjacent OFDM symbols in thetime domain within the resource block, at least two subcarriers on whichthe pilot is transmitted are on one of the plurality of OFDM symbols ofthe resource block, and the pilot is transmitted: on at least three ofthe plurality of OFDM symbols of the resource block, and on subcarriersthat include a subcarrier of a highest frequency and a subcarrier of alowest frequency in the frequency domain respectively on the at leastthree OFDM symbols within the resource block; and a demodulatorconfigured to demodulate the signal by using the pilot, wherein theorthogonal sequence is selected based on a set of orthogonal sequencesrepresented by an n×n matrix, n being a positive integer, wherein rowsof the matrix constitute the orthogonal sequences.